1. Field of the Invention
The present invention relates to optical devices, hole transporting polymers therefore, and the manufacture of such polymers from polymerizable units. The invention further relates to a process for the preparation of such polymerizable units.
2. Related Technology
Organic light emissive devices generally comprise a cathode, an anode and an organic light emissive region between the cathode and the anode. Light emissive organic materials may comprise small molecular materials such as described in U.S. Pat. No. 4,539,507 or polymeric materials such as those described in PCT/WO/13148. The cathode injects electrons into the light emissive region and the anode injects holes. The electrons and holes combine to generate photons.
Organic photovoltaic devices also generally comprise a cathode, an anode and an organic photoresponsive region between the cathode and the anode. Such devices are described in WO96/16449. The photoresponsive region absorbs light and creates pairs of electrons and holes which are collected by the electrodes, forming an electric current which can be used to drive an electronic device.
FIG. 1 shows a typical cross-sectional structure of an optical device. The device is typically fabricated on a glass or plastics transparent substrate 1 coated with a transparent anode 2 such as an indium-tin-oxide (ITO) layer. The ITO coated substrate is covered with at least a layer of a thin film of a photoresponsive or electroluminescent organic material 3 and a cathode material 4 of low work function metal such as calcium is applied, optionally with a capping layer of aluminum (not shown). Other layers may be added to the device, for example to improve charge transport between the electrodes and the photoresponsive or light emissive material. The device shown is a light emissive device with a power source connected to the electrodes. In a photovoltaic device the electrodes would be connected to the device to be driven.
A charge transport layer which is often used in electroluminescent and photovoltaic devices is a hole transport layer situated between the anode and the light emissive or photoresponsive region. This layer transports holes from the anode to the light emissive or photoresponsive region. Polyethylene dioxythiophene (PEDOT) is a material generally used for this layer which provides an energy level between indium tin oxide at the anode and, say, PPV as the emissive material. PEDOT is disclosed in EP0686662. PEDOT is a polythiophene which is electron-rich and therefore useful as a hole transporting polymer.
Hole and electron transport to a light emissive region of an optical device is discussed in WO00/55927. According to this disclosure, rather than have hole and/or electron transport regions formed from discrete layers in a multilayer device, one or both of the hole and electron transporting regions is formed in a single polymer. Various monomeric repeat units are proposed for use in this arrangement, including terthiophene units. However, the approach is limited by the availability of monomer units and their ability to be polymerized according to the methods described. No synthetic route to thiophene-rich polymers is described.
Outside of the field of optical devices, polyarylenes with pendant trifluoromethyl groups have been described by Banerjee et al in Polymeric Materials Science and Engineering (1999), 80, 98-99. Rigid rod polymers useful for their high mechanical strength are described. Various triaryl monomers were synthesized by palladium catalyzed cross-coupling of 4-chloro-3-trifluoromethyl phenyl boronic acid with dibromo benzene, pyridine and thiophene compounds. These monomers were polymerized to form polymers.
A need exists for the provision of novel hole transporting polymers for use in optical devices. Accordingly, in a first aspect, the invention provides a process for the preparation of a polymerizable unit for production of a hole transporting polymer for use in an optical device, which process comprises reacting
in the presence of S to form
wherein each R is the same or different and is independently H or a substituent group; n is O or an integer from 1 to 100; Ar and Ar′ are the same or different and are each aromatic orheteroaromatic groups which are substituted or unsubstituted; Y is a direct bond, a light emissive moiety, a hole transporting moiety or an electron transporting moiety; and X is a polymerizable group.
The invention further provides a process for the preparation of a hole transporting polymer for use in a optical device by polymering a polymerizable unit prepared as described above, optionally in the presence of at least one other polymerizable unit.
The hole transporting polymer prepared as described above may be used in an optical device. The invention also provides an optical device and a process for manufacturing the same.